But another aspect of Komen's activities hasn't received much attention: Komen's position on research using human embryonic stem cells.

Despite raising millions of dollars for breast cancer research, Komen hasn't funded any of this work, prompting questions about whether that decision is rooted in politics.

"We find this disappointing and really fairly ironic for a group that is 'for the cure' to walk away from research that many scientists think could unlock cures for diseases, including cancer," said Sean Tipton of the Coalition for the Advancement of Medical Research, which lobbies for research with human embryonic stem cells.

Many scientists think human embryonic stem cells could lead to cures for many ailments, including heart disease, diabetes, some forms of blindness and possibly cancer. But human embryos have been destroyed to obtain some of the cells. So the research has long been controversial.

"Anything that involves reproductive biology, whether it's a sex survey among high school students or it's contraceptive services, abortion, immediately stirs up political passions," said Daniel Greenberg, who studies the intersection of science and politics.

No one from Komen agreed to be interviewed for this story. But officials maintained that the group doesn't have a formal ban on research involving human embryonic stem cells. They say they just haven't found anything worth funding yet.

But Tipton and others say there are many ways stem cells could help fight breast cancer. "Embryonic-stem-cell work is a powerful research tool for all kinds of diseases and conditions, and breast cancer would certainly be one of those candidates," Tipton said.

For example, stem cells could be used to study the genetic causes of breast cancer, decipher the basic biology of breast cancer tumors and perhaps test new drugs to treat the disease, Tipton and others said.

"Funding science is supposed to be based on merit," said George Q. Daley, a stem-cell researcher at Harvard University. "Scientific funding should support the best ideas. And if someone has a brilliant idea relevant to breast cancer research or heart disease that uses human embryonic stem cells, it'd be a huge lost opportunity to have one of these foundations refuse to fund it."

Charitable groups can be skittish about politically sensitive research because of fears of alienating some of the legions of volunteers and donors they depend on for survival, Greenberg said.

"These groups live on handouts from the public and they are very, very concerned about offending any donors or potential donors. It's very easy to scare them off," Greenberg said. "Various groups that have a particular issue to push know about this sensitivity and vulnerability of charitable organizations and they're able to manipulate it very well."

Rose Marie Robertson, chief science officer at the American Heart Association. acknowledged that embryonic stem cells could lead to breakthroughs for the nation's leading killer. That's why, she said, her group supports federal funding of the research. But the heart association has banned funding the work itself because of fears of offending volunteers and donors.

"There are people who have varying views in terms of whether they find this personally or ethically, or from a religious perspective, something that is reasonable," Roberton said. "If, in fact, donors chose not to support the heart association because of a particular view in terms of human-embryonic-stem-cell research that would really be harmful."

The American Cancer Society wouldn't make anyone available for an interview. In a statement, the group said it funds research into promising alternatives to human embryonic stem cells. But the "nature" of human embryonic stem cell research "make it imperative that it be pursued under appropriate protections," the groups said. And the federal government, not the cancer society, is "best suited" to "oversee it," according to the statement.

Shots is the online channel for health stories from the NPR Science Desk. We report on news that can make a difference for your health and show how policy shapes our health choices. Look to Shots for the latest on research and medical treatments, as well as the business side of health. Your hosts are Scott Hensley and Nancy Shute. You can reach the Shots team via our contact form.